To simplify code development for various international markets, the Microsoft run-time library provides Microsoft-specific "generic-text" mappings for many data types, routines, and other objects. These mappings are defined in TCHAR.H. You can use these name mappings to write generic code that can be compiled for any of the three kinds of character sets: ASCII (SBCS), MBCS, or Unicode, depending on a manifest constant you define using a #define statement. Generic-text mappings are Microsoft extensions that aren't ANSI compatible.
Preprocessor directives for generic-text mappings
#define
Compiled version
Example
_UNICODE
Unicode (wide-character)
_tcsrev maps to _wcsrev
_MBCS
Multibyte-character
_tcsrev maps to _mbsrev
None (the default: both _UNICODE and _MBCS not defined)
SBCS (ASCII)
_tcsrev maps to strrev
For example, the generic-text function _tcsrev, defined in TCHAR.H, maps to mbsrev if MBCS has been defined in your program, or to _wcsrev if _UNICODE has been defined. Otherwise _tcsrev maps to strrev.
The generic-text data type _TCHAR, also defined in TCHAR.H, maps to type char if _MBCS is defined, to type wchar_t if _UNICODE is defined, and to type char if neither constant is defined. Other data type mappings are provided in TCHAR.H for programming convenience, but _TCHAR is the type that is most useful.
Generic-Text Data Type Mappings
Generic-text data type name
SBCS (_UNICODE, _MBCS not defined)
_MBCS defined
_UNICODE defined
_TCHAR
char
char
wchar_t
_TINT
int
int
wint_t
_TSCHAR
signed char
signed char
wchar_t
_TUCHAR
unsigned char
unsigned char
wchar_t
_TXCHAR
char
unsigned char
wchar_t
_T or _TEXT
No effect (removed by preprocessor)
No effect (removed by preprocessor)
L (converts following character or string to its Unicode counterpart)
For a complete list of generic-text mappings of routines, variables, and other objects, see Generic-text mappings.
The following code fragments illustrate the use of _TCHAR and _tcsrev for mapping to the MBCS, Unicode, and SBCS models.